PATH-53. ANAPLASTIC PLEOMORPHIC XANTHROASTROCYTOMA WITH BEND5-NTRK2 FUSION IN A YOUNG ADULT WITH A HISTORY OF CRANIAL RADIATION FOR CHILDHOOD RHABDOMYOSARCOMA

Abstract

Abstract INTRODUCTION: Pleomorphic xanthoastrocytoma (PXA) is a rare subset of circumscribed astrocytic glioma. While PXA typically has a favorable prognosis, anaplastic (WHO Grade III) PXA (aPXA) has a poorer prognosis. Molecular analysis of PXA often reveals BRAF mutations or CDKN2A/B homozygous deletions. NTRK fusions have been identified in a few cases of pediatric gliomas including PXA. BEND-5 gene alterations have been rarely reported in CNS tumors such as glioblastoma but have not been previously reported in PXA. Case Presentation The patient is a 24-year-old female with history of nasopharyngeal embryonal rhabdomyosarcoma treated with chemotherapy and radiation at age 3. She was tested for Li-Fraumeni Syndrome and was reportedly negative. One year ago, she presented with visual changes and was found to have an occipital aPXA. She underwent a gross total resection but declined further treatment with radiation. Next-generation sequencing (NGS) identified a BEND5-NTRK2 fusion, and she began treatment with Larotrectinib. Serial MRI scans have shown no evidence of disease recurrence. Discussion Pediatric patients are at increased risk for glioma after radiation which is age- and dose/volume-dependent. Radiation-induced gliomas are typically higher grade, present in atypical sites, and have a poor prognosis. Development of PXA following radiation is rare but has been reported. Our patient was diagnosed with aPXA almost 20 years after initial treatment for rhabdomyosarcoma. Her aPXA exhibited a BEND5-NTRK2 fusion and lacked classical BRAF alterations and CDKN2A/B deletions that are present in de novo cases. A Neuro-Onc Panel did not identify her fusion or include testing for BEND5 alterations. However, an expanded RNA Exome Fusion Panel NGS identified a unique fusion, which opened her up to targeted treatment with an NTRK inhibitor. Our patient is now 1 year from resection without disease progression on larotrectinib. This case highlights the importance of expanded NGS testing, particularly in rare tumors.